Since polyphenylene ethers are excellent in processability and productivity, products/parts of any shape can be produced efficiently from them by melt injection molding, melt extrusion and the like. They are therefore widely used as a material for products/parts in the electric/electronic fields, automotive field, various other industrial material fields, or food/package fields.
With recent trends in the production of a variety of products/parts particularly in the electric/electronic fields, automotive field or various other industrial fields, the demand for resin materials has increased.
In order to satisfy this demand, resin materials having properties that have not been hitherto attained in existing materials have been developed by forming a composite from different materials or by a polymer alloy technique using various existing polymer materials in combination.
Although ordinarily employed polyphenylene ethers have high heat resistance and excellent mechanical properties, materials that form composites with polyphenylene ethers are limited owing to their poor affinity for other materials. Affinity with a highly polar material such as polyamide is particularly poor so that a modified polyphenylene ether resin having polar group functionality is required upon formation of a composite with such a resin.
As means for obtaining a modified polyphenylene ether resin, chemical modification, in a molten state, of a polyphenylene ether or polyphenylene-ether-containing resin composition with a compound having a polar group is under investigation.
For example, proposed in JP-B-3-52486 (the term “JP-B” as used herein means an “examined published Japanese patent publication”), U.S. Pat. No. 4,654,405, U.S. Pat. No. 4,888,397 or JP-A-63-54425 (the term “JP-A” as used herein means an “unexamined published Japanese patent application) is a process for obtaining a modified polyphenylene ether resin by mixing a polyphenylene ether with maleic anhydride or another reactive compound for modification in the presence or absence of a radical initiator, and kneading the mixture in a molten state.
The above-described process however causes various problems, because kneading of the polyphenylene ether in a molten state requires high temperature and the melt viscosity of the polyphenylene ether is very high, which inevitably cause a marked rise in the reaction temperature.
In other words, a modified polyphenylene ether resin obtained by the conventional melt kneading method is processed at almost the decomposition temperature so that a color change due to thermal deterioration occurs and the modified polyphenylene ether resin thus obtained suffers a problem in its color tone/appearance.
In order to overcome the above-described problem in color tone/appearance, there has been proposed a process for melt extrusion of a mixture of a polyphenylene ether and an additive such as heat stabilizer and antioxidant. This process however fails in achieving sufficient improvement in color tone/appearance because the temperature upon melt kneading is unduly high.
In U.S. Pat. No. 5,159,027, there is disclosed a polyphenylene ether resin having a specific cyclic end group which resin is available by melt kneading a polyphenylene ether having a specific end structure and a compound having functionality. While the number of Fries rearrangement structures in the ordinarily employed polyphenylene ether is 0.18 or greater per 100 recurring units of the resin, the number of such structures in this polyphenylene ether resin can be reduced to 0.01 per 100 recurring monomer units of the resin. It is reported that this resin has therefore excellent color tone.
The above-described technique however cannot produce a highly functional polyphenylene ether resin having Fries rearrangement structures reduced in number to less than 0.01 per 100 recurring units.
In addition, the Fries rearrangement can be suppressed only when the polyphenylene ether has a specific cyclic end group so that the above-described technique is not sufficient for obtaining a highly functional polyphenylene ether resin.
As another technique for improving color tone/appearance, conventionally employed is addition of a plasticizer such as mineral oil to a polyphenylene ether, thereby lowering the processing temperature upon melt extrusion. The resulting modified polyphenylene ether resin, when molded or formed, has improved color tone/appearance but has deteriorated heat resistance/mechanical physical properties.
Thus, modified polyphenylene ether resins available by the prior art do not satisfy the demands of industry, because they have drawbacks in equipment/energy or are not sufficient in the balance between color tone/appearance and heat resistance/mechanical physical properties.
The present invention therefore relates to a modified polyphenylene ether resin and a process for preparing same. An object of the present invention is to provide a modified polyphenylene ether resin which exhibits sufficient functionality, is free from problems in equipment or energy, assures well-balanced color tone/appearance and heat resistance/mechanical physical properties, and can satisfy the demands of industry sufficiently.